Question

What weights of p4o6 and p4o10 will be produced by combustion of 31g p4 in 32g o2 leaving no p4 and o2

Answer 1

 P4O6 = 56.3437% P 
P4O10 = 43.6420% P 
31 g P = 31 / (31 + 32) = 49.2063% P 

So it becomes a problem in proportions: 
100% P4O6 = 56.3437% 
z% P4O6 = 49.2063% 
0% P4O6 = 43.6420% 
Find z. 

z / 100 = (49.2063 - 43.6420) / (56.3437 - 43.6420) 
Solve for z algebraically: 
z = 43.808% P4O6 

By the Law of the Conservation of Matter, the total mass 
of P4O6 and P4O10 = 31g + 32g = 63g 

43.808% of 63g = 27.6 g P4O6 
63g - 27.6g = 35.4 g P4O10